1. Field of the Invention
The present invention relates to a method for manufacturing a thermally-assisted magnetic recording head used for thermally-assisted magnetic recording in which a portion to be written of a magnetic recording medium is heated and thus writing is performed to the portion where anisotropic magnetic field decreases. The present invention especially relates to a method for manufacturing a thermally-assisted magnetic recording head constituted by joining a light source unit and a slider. The present invention further relates to an apparatus used for the joining.
2. Description of the Related Art
With the explosion in the use of the Internet in these years, a huge amount of data that are incommensurably larger than ever are stored and used on computers such as servers and information processing terminals. This trend is expected to further grow at an accelerated rate. Under these circumstances, demand for magnetic recording apparatuses such as magnetic disk apparatuses as mass storage is growing, and the demand for higher recording densities of the magnetic recording apparatuses is also escalating.
In the magnetic recording technology, it is necessary for magnetic heads to write smaller recording bits on magnetic recording media in order to achieve higher recording densities. In order to stably form smaller recording bits, perpendicular magnetic recording technology has been commercially implemented in which components of magnetization perpendicular to the surface of a medium are used as recording bits. In addition, thermally-assisted magnetic recording technology that enables the use of magnetic recording media having higher thermal stability of magnetization is being actively developed.
In the thermally-assisted magnetic recording technology, a magnetic recording medium formed of a magnetic material with a large energy KU is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion; just after that, writing is performed by applying write field to the heated portion. Actually, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light (NF-light). In this case, it is significantly important where and how a light source with a sufficiently high light output should be disposed inside a head in order to stably supply a light with a sufficiently high intensity at a desired position on the magnetic recording medium.
As for the setting of the light source, for example, U.S. Pat. No. 7,538,978 B2 discloses a configuration in which a laser unit including a laser diode is mounted on the back surface of a slider, and US Patent Publication No. 2008/0056073 A1 discloses a configuration in which a structure of a laser diode element with a monolithically integrated reflection mirror is mounted on the back surface of a slider.
The present inventors propose a thermally-assisted magnetic recording head with a “composite slider structure” which is constituted by joining a light source unit provided with a light source to the end surface (back surface) of a slider provided with a write head element, the end surface being opposite to the opposed-to-medium surface of the slider. The “composite slider structure” is disclosed in, for example, US Patent Publication No. 2008/043360 A1 and US Patent Publication No. 2009/052078 A1. The advantages of the thermally-assisted magnetic recording head with the “composite slider structure” are as follows:
a) The head has an affinity with the conventional manufacturing method of thin-film magnetic heads because the opposed-to-medium surface and the element-integration surface are perpendicular to each other in the slider.
b) The light source can avoid suffering mechanical shock directly during operation because the light source is provided far from the opposed-to-medium surface.
c) The light source such as a laser diode and the head elements can be evaluated independently of each other; thus the degradation of manufacturing yield for obtaining the whole head can be avoided; whereas, in the case that all the light source and head elements are provided within the slider, the manufacturing yield rate for obtaining the whole head is likely to decrease significantly due to the multiplication of the process yield for the light-source and the process yield for the head elements.
d) The head can be manufactured with reduced man-hour and at low cost, because of no need to provide the head with optical components such as a lens or prism which are required to have much high accuracy, or with optical elements having a special structure for connecting optical fibers or the like.
It is important to appropriately join a light source unit to a slider in fabricating the thermally-assisted magnetic recording head having the “composite slider structure”. Specifically, it is essential to provide a sufficiently strong junction, to provide a heat dissipation path for the light source after the joining, and to ensure a sufficiently high accuracy of joining position.
A sufficiently strong junction can be provided by using metal solder to join the light source unit and the slider. In this case, the light source unit and the slider sandwich the metal solder therebetween. This arrangement can provide a heat dissipation path along which heat radiated from the light source is transferred sequentially to the unit substrate, the metal solder, the slider substrate, and a magnetic recording medium during write operations of the head flying above the magnetic recording medium.
When metal solder is used for the joining, the layer of the metal solder needs to be formed to an appropriate thickness, for example a thickness in the range of approximately 0.05 to 2 μm (micrometers). If the solder is too thin, it is difficult to provide sufficient joining strength. On the other hand, if the solder is too thick, the distance between the light source unit and the slider will be so large that light emitted from the light source significantly attenuates before reaching an optical system in the slider, possibly resulting in a significantly reduced light use efficiency of the head. In addition, solder can flow into the space between the light source and the optical system.
When solder with such limitations of thickness is used to join the light source unit and the slider, it is important to provide extremely high “conformity” between the joining surfaces of the light source unit and the slider. The term “conformity” as used here means the degree of parallelism of a surface to a reference surface, or the degree to which a surface conforms to a reference surface. Suppose that the joining surface of a light source unit that is 500 μm wide in the track width direction is to be joined to the joining surface of a slider that is well wider than the joining surface of the light source unit. If alignment conducted before joining is completed with the joining surface of the light source unit being tilted at a small angle of 0.5° (degree) to the joining surface of the slider and then the solder is melted to complete the joining, one end of the joining surface of the light source unit will be at a distance of at least approximately 4.4 μm apart from the joining surface of the slider. Even if the solder is 2 μm thick, a gap will be formed between the joining surfaces and the strength of the joining can be unacceptably reduced. If the joining is weak, the light source unit can become detached from the slider during a subsequent process step such as a cleaning step, or during use of the head.
A sufficiently high accuracy of joining position between the light source unit and the slider can be achieved by active alignment. Here, the active alignment is a method in which a light source such as a laser diode is actually put into operation and, while the light source and an optical system such as a waveguide are moved relatively to each other, light emitted from the light source and incident on the light-receiving end of the optical system is monitored on the light-emitting end side of the optical system in real time until the light intensity in the monitoring location is maximized, then the maximum intensity position is set as the desired relative position of the light source with respect to the optical system. The active alignment requires that electric power be supplied to the light source of the light source unit by pressing probes against electrodes for the light source while the light source unit is being moved above the slider. There is a method for meeting the requirement in which the light source is held with a clamp in such a manner that the surface of the light source unit on which the electrodes are formed is not covered with the clamp, and the clamp holding the light source unit is moved above a stage on which the slider is placed to align the light source unit to the slider.
However, it is difficult to sufficiently increase the conformity between the joining surfaces of the light source unit and the slider by this method of moving the light source. In fact, the surfaces of the unit substrate of the light source unit have errors in squareness to each other due to working accuracy limitations. In addition, the surfaces of the clamp that hold the light source unit also have errors and the movement of clamp with respect to the stage also has an error due to adjustment limitations. Therefore, even when the clamp is moved closer to the stage to bring the light source unit into contact with the slider, it is significantly difficult to achieve high conformity between the joining surfaces of the light source unit and the slider. If a conformity adjustment mechanism such as an air gimbal is provided in the stage in order to address the conformity problem, the mechanism will have little effect in adjusting conformity because the size of the slider placed on the stage is very small. The mechanism also adds complexity to the joining apparatus.
As will be appreciated from the foregoing, there is an intense need for a method capable of achieving an extremely high “conformity” between the joining surfaces of the light source unit and the slider in joining between the light source unit and the slider after aligning the light source unit and the slider with each other by active alignment.